Press Release

Can Printed Electronics Replace PCB Technology?

In the last Bleeding Edge column, I covered a few of the very basic points of printed electronics. What we must realize is that there are many very different printed electronics applications, and each application has vastly different requirements as to the technologies required.

We will ignore all the solar, keypad, luminescent and battery applications for now and concentrate mainly on possible PCB replacement technologies.

A quick recap on PCB replacement conductive ink technologies:

The old standby silk screening can lay down a reasonably fine line of conductive ink, but not without some difficulty. The line widths in the 5/5 are obtainable, but we run into a serious problem with high-resistance lines, shorts from bleeding and misprinting.

As we require lower resistance than a single printed conductive ink screen trace can provide, it would therefore seem not suitable for normal PCB replacement. Nano inks may help lower the resistance numbers, but the problems with screening accuracy and bleeding will limit its applications. Silk screening will always be able to replace some single-sided low-current applications, but not the 3 mil fine-line higher-density 12-layer boards of today.

Inkjet printing is the newcomer in the PCB business; I would put the technology at the working, 'good promise' stage, with a few inkjet machines already in the marketplace. There exists a good representative market similar to that for conductive inks, with white marking ink machines in service for the last four years and upcoming soldermask inkjet units waiting to be finished.

Some companies are working on inkjet conductive ink programs now. They illustrate a few good and bad points associated with this technology. The first problem relates to the size of the conductive particle. To be properly sprayed in droplets of the right size and pass through the inkjet head, the conductive particles of silver, copper or gold must be between 100 nanometers and 40 nanometers in size.

In silkscreen printing, the screen can pass a larger particle, so we can use bigger 10 micron particles to lower costs. The difficulty in manufacturing the nano-sized conductive particles is reflected in the higher cost. Inkjet developers will need to address the ink cost problem in the future to be successful.

Another inkjet problem is the small amount of copper conductive ink that is laid down, resulting in a thin line that creates a high resistance problem for circuits requiring more power. However some nano copper liquids for inkjets can be fused together at 180ºC to 280º C, creating a more solid line with lower resistance.

This resistance is more in line with the plated copper we have used for years.